The invention relates generally to methods and systems by which power utility companies can reduce power demand by utility customers, and more particular to automatic methods and systems by which a utility can selectively terminate output of high voltage (220 VAC) power while continuing to provide low voltage (120 VAC) power to utility customers.
Millions of electrical power users in the western United States and especially in California have experienced the crisis that can arise when the demand for electrical power exceeds the ability of power utility companies to generate and distribute such power. Millions of customers experienced xe2x80x9crolling blackoutsxe2x80x9d during which no electrical power was made available to residential and even large businesses in certain regions that were identified in advance. In other instances, electrical power was made available but at exorbitantly high cost per kilowatt/hour. States and other public entities paid billions of dollars to obtain emergency electrical power, and even then many customers went without power at all times. Further, many users went to great extremes and inconvenience to voluntarily reduce power consumption during the time of such crisis. In addition to the inconvenience of substantially curtailed electrical consumption, and the high price of such power as was consumed, many commercial businesses sustained substantial economic losses due to the energy crisis.
FIG. 1A typifies the power distribution system common used throughout North America for most homes and small businesses. The power company (UTILITY) generates high voltage (HV), typically many tens of thousands of volts of alternating current (AC) voltage, that it distributes across power lines suspended from utility poles. Standard distribution transformers XFMR are used to step-down the high voltage to provide two lower voltage xe2x80x9chotxe2x80x9d lines denoted T1 and T2, and a ground or neutral line T3. Lines T1, T2, T3 typically interface from transformer XFMR via a metal conductor power block 10 and are brought into a user""s facility (e.g., USER-1, . . . , USER-n) via customer or user input lines P1, P2, P3 respectively via a power panel (20-1, . . . 20-n), associated with each user""s facility.
Each power panel is defined as having two banks, Bank 1, Bank 2, as best seen in the schematic representation of FIG. 1B. As shown in FIG. 1B, the T3 output line of the distribution transformer is coupled to ground, usually near the transformer, and the user line P3 is coupled to ground, usually near the power panel. While FIGS. 1A and 1B depict only two user""s receiving power from a single distribution transformer, in practice more than two users are serviced by a single distribution transformer. The relationship between the various voltage phases is shown in FIG. 1C. T1 and T2 each carry one phase of 120 VAC 60 Hz relative to T3 and are 180xc2x0 out of phase relative to one another. Thus, an electrical connection between T1 and T3 or between T2 and T3 will provide 120 VAC, whereas an electrical connection between T1 and T2 will provide 240 VAC.
Most household appliances operate from 120 VAC, and will receive potential from Bank 1 or Bank 2, e.g., from T1 relative to T3 or from T2 relative to T3. However some appliances require higher operating power such as air conditioners, electric water heaters, electric ranges, electric clothes dryers, etc. and are intended to receive 240 VAC. Such appliances are provided with 240 VAC from Bank 1 to Bank 2, e.g., from T1 to T2. (Understandably, an appliance that consumes say 2 KW of electrical power requires half the current when operated at 240 VAC than when operated at 120 VAC.)
FIG. 1D depicts a customer power panel 20-x and shows the equivalent circuit of the various customer loads that may be present across lines P1-P3, and/or P2-P3, and/or P1-P2. It is understood that the equivalent circuit of the various loads may be inductive, resistive, capacitive, or some combination thereof. In FIG. 1D, load L 120 B-1 represents the appliances or other loads coupled to receive Bank 1 120 VAC at the customer""s location. Load L 120 B-2 represents loads coupled to receive Bank 2 120 VAC at the customer""s location, while load L 240 represents loads coupled to receive 240 VAC at the customer""s location, perhaps an electric oven and an electric water heater. All three loads are shown with cross-hatching to depict that they can receive operating potential via power panel 20-x.
In an attempt to reduce power consumption during high demand periods or crises, utility companies have attempted to implement systems to reduce power consumed by certain users, without terminating all of the user""s power. Such prior art attempts have included installing special remote-controllable switches on air conditioners. Upon receipt of a control signal, e.g., via radio or special telephone, a relay can de-couple such appliances from the AC power lines, thus reducing peak power, while still permitting other appliances within the user""s facility to operate. But such attempts require installation of literally millions of such remote-controllable switches, and require customer approval.
What is needed is a more efficient system to allow a power utility to reduce user peak power demand. Preferably when user locations do not have so-called branch wiring, such system should be implemented and operable without having to install remote-controllable switches at each user location. Preferably such system should be operable, without prior customer approval, to reduce or eliminate consumption of 240 VAC, while still permitting normal consumption of 120 VAC.
The present invention provides such a system.
The present invention provides a load reduction switch (LRS) and a switch controller that can reconfigure the LRS in response to a utility-issued input signal. The LRS and switch controller are coupled, electrically, downstream from a distribution transformer and upstream from a user facility, either before or after, or indeed within, the user""s power meter. The distribution transformer outputs out-of-phase 120 VAC on T1 and T2 lines (for respective Bank 1 and Bank 2 voltage supply), and further includes a neutral T3 line. Relevant consumer locations normally are coupled via user lines P1, P2, P3 to the T1, T2, T3 lines. In use, one active line, e.g., T2 is always connected to P2, but the T1-to-P1 connection is controlled by the configuration of the LRS. In normal mode, the LRS maintains the T1-P1 connection, and the user can obtain 120 VAC and 240 VAC.
In one embodiment, during a first mode of operation, the LRS disconnects P1 from T1 and simply allows P1 to float. In this mode, 120 VAC is available at Bank 2, but normally there will be neither 120 VAC at Bank 1, nor 240 VAC provided to the user. If a user 120 VAC appliance is turned-on and coupled to Bank 1, and if a user 240 VAC appliance is also turned-on and coupled across Bank 1 and Bank 2, such turned-on appliances will attempt to share a total of 120 VAC, but no 240 VAC will be present. In that embodiment, during a second mode of operation, the LRS couples P1 to T2 (and thus to P2), and in-phase 120 VAC is available at Bank 1 and Bank 2, but again no 240 VAC is provided to the user. Some consumer locations have so-called branch circuit wiring in which a common neutral line returns current delivered to loads via the P1 line or the P2 line. In such installations, current-limiting devices are placed in series with the P1 and P2 lines. These devices prevent an excessively high magnitude of in-phase resulting from the summation of the and P2 line currents from passing through the common neutral return line.
In a more favored embodiment, the LRS functions as a double pole double throw switch. In normal operation, the LRS connects T1 to P1, and T2 to P2, thus providing Bank 1 and Bank 2 of 120 VAC, and 240 VAC. But in a power conservation mode, the LRS is reconfigured such that T1 floats, and P1 is connected to P2, and collectively P1 and P2 are coupled via a current limiting device to T2. This mode of operation provides in-phase 120 VAC to Bank 1 and Bank 2, but no 240 VAC.
By commanding the LRS to reconfigure via the switch controller, a power utility company can cut-off delivery of 240 VAC to users, and can, if desired, eliminate one Bank of 120 VAC to users. The LRS and/or controller unit may be disposed on a utility power pole, adjacent the distribution transformer, or at a user facility, for example within the user""s power meter. The LRS may be implemented as a mechanical switch and/or as a switch comprising solid state devices.
Other features and advantages of the invention will appear from the following description in which the preferred embodiments have been set forth in detail, in conjunction with the accompanying drawings.